Calling directory inquiries used to be a simple, if expensive, matter of dialling 192 and jotting down the requisite numbers.

But from the end of August calling 192 will no longer be an option, after telcoms watchdog Oftel opted to discontinue the service, a hangover from BT's days as a monopoly.

At least 13 directory inquiry services have already been launched to compete for business, but by August there could be an avalanche of operators vying for custom.

According to Oftel, 84 companies have applied to register a "new 192" service with applications for more than 300 different numbers.

It is a far cry from a decade ago, when there was just one operator, one number and no charge. Customers, while used to paying for directory inquiries, will now face charges ranging from 20p to 85p to get the telephone number of a friend, a business or a local plumber.

The new six-digit numbers, which all start with 118, have been available since December last year, but the marketing push to promote them is already in overdrive with full-page adverts in the weekend press.

One advert unveiled BT's new number and another, confusingly, unveiled a similar number for a service described as "not BT (thank goodness)".

The rivalry is set to intensify in the run-up to the end of August when 192, which is still running in conjunction with the new numbers, will cease to exist. BT will then compete against other providers with its own 118 service, which is already up and running.

A raft of new services have already launched, with many of them advertising in the weekend press, on billboards and on the underground in London.

Each new directory inquiries number begins with 118, followed by a new three digit code.

But with each new operator charging different amounts, and operating various tariffs depending on whether they charge a fixed fee or a per-minute charge, the new system is bound to leave the average consumer baffled.

Key in the wrong number on a mobile phone, and customers could end up paying more than BT's existing 40p one-off charge.

For users who are unaware of the changes or have not studied the small print, the new services will become a lottery - they could end up saving money or paying as much as £2 for a call.

The deregulation of directory inquiries, which was intended to save users money, is already shaping up to be a major consumer battle with echoes of the cash machine charging PR fiasco two years ago.

The situation becomes even more confusing when calls are made from a mobile phone, with a complex charging arrangement between the new directories services, the mobile networks and the user.

From a mobile phone, the four main networks are keen to ensure that their customers continue to phone their own directories services and don't defect to the competition.

But with so many services vying for the customer's attention, it will be easy to accidentally call the most expensive option - a directory service operated by a rival mobile phone company.

Consumers who find a new service that is good value from their home phone while out and about may find themselves landed with bills of up to 85p a minute when they use the same number from their mobile.

Customers have no way of knowing how much they are going to pay for directory inquiries until they get their first bill.

A spokesman for The Number, one of the 13 new directories services, said it was pushing for mobile operators to publish their tariffs for connecting customers to the new services. But he warned that calling from a mobile could end up costing around £2 for the average call.

He also conceded that the industry should be doing more to make matters clearer for the consumer.

"It's just so complicated. There's no overall campaign from an independent and reliable source that says what is happening and what it's going to mean for customers," he added.

Oftel has launched a website to inform consumers about the changes, but is not planning any mainstream advertising.

The waters are muddied further because many of the new services offer the option of connecting the caller to their required number, for which a further per-minute charge is levied.

Many of the new services are also hoping to bring in additional revenue by offering new services such as cinema listing information, texting numbers to the caller's mobile and searching local classified listings for the nearest plumber, dentist or florist.